1. Field of the Invention
This invention relates to an apparatus of and a method for image reproducing with variable reproduction scale used in image scanning and recording systems such as monochrome scanner and facsimile machines, and more particularly to an apparatus of and a method for image reproducing with variable reproduction scale capable of scanning and recording an original image as enlarged or reduced in size.
2. Description of the Prior Art
A method for image reproducing with variable reproduction scale prior to the present invention is disclosed in Japanese Patent Publication No. 60-37464, for example. According to this publication, pixel dot data of an original image corresponding to a single scan line are written in time series into a buffer memory. When reproducing the image, the pixel dot data are read out from the memory as follows. For enlarging the image, a read-out address is repeatedly applied to the buffer memory with a predetermined frequency corresponding to a desired magnification. For reducing the image, the read-out address application is skipped. The number of pixel dot data is thereby increased or decreased for output to a recording head for exposing a photosensitive film. As a result, an enlarged or reduced reproduced image is obtained.
The concept of the term "interpolation" appearing later in this specification is explained now. The term interpolation as used herein embraces the "addition" and "skipping" of pixel dot data. Further, the pixel dot data include not only binary pixel data as expressed in "H" and "L" but tints having a uniform half tone distribution of dots.
A specific example of methods for reproducing an enlarged or reduced image will be described referring to FIG. 13. Pixel dot data S1, S2, S3, S4 and so on are written into a buffer memory. It is assumed here that the image is enlarged by 1.25 times. Since 1.25 is 5/4, an interpolation pattern is set to repeat "1, 1, 1 and 2" as a reference pattern for determining the number of times each pixel dot data is read out.
In reading out four pixel dot data S1, S2, S3 and S4, they are read out, for example, as S1, S2, S3, S4 and S4, with S4 added once. Subsequently, the pixel dot data S4 is likewise added cyclically once in every four times. As a result, the original image is reproduced in a 1.25 times enlargement.
When the original is reduced by 0.75 times, the following operation is carried out. Since 0.75 is 3/4, an interpolation pattern for repeating "1, 1, 1 and 0" is set as a reference. The "0" here means skipping of the pixel dot data. For the four pixel dot data S1, S2, S3 and S4, data S1, S2 and S3 are read out skipping S4. Subsequently, the pixel dot data S4 is likewise skipped cyclically once in every four times. As a result, the original image is reproduced in a 0.75 times reduction.
The above addition or skipping is carried out whether pixel dot data Si is "H" (black) or "L" (white). The interpolation pattern serving as the reference is variable with magnification.
In conventional practice, as described above, the position for interpolating the data is fixed by the interpolation pattern calculated for each magnification. The original image, therefore, is subjected to interpolation every several pixels when an original image is enlarged or reduced by a magnification not expressed in an integer. As a result, the interpolated pixels constitute pattern elements absent from the original image. Such example are shown in FIGS. 14A through 14C. FIG. 14B shows an enlarged reproduction of the original image shown in FIG. 14A, which is obtained by enlarging the latter in a main scanning direction by 1.25 times in the manner illustrated in FIG. 13. FIG. 14C shows a reduced reproduction of the original image of FIG. 14A obtained by reducing the latter by 0.75 times.
As shown in FIG. 14B, one pixel is added to every fourth pixel output when the original image is enlarged by 1.25 times. On the other hand, as sown in FIG. 14C, the pixel dot data for every fourth pixel is omitted when the original image is reduced by 0.75 times.
Regular patterns will appear in portions enclosed with solid lines in each reproduced image. These patterns constitute interfering streaks out of harmony with the rest of the image, and deteriorate image quality. In the examples shown in FIGS. 14B and 14C, the magnification is effected in the main scanning direction only. The reason is that, in a copying machine or the like, magnification is effected in the subscanning direction by varying the scan speed.
When the original image is enlarged by the number of times expressed in an integer, all the dot data are repeated that number of times, thereby interpolating all pixels evenly. Consequently, the above-noted problem will not arise.